IDENTIFICATION OF A NOVEL GENE, DEP, ASSOCIATED WITH DEPOLYMERIZATIONOF THE CAPSULAR POLYMER IN BACILLUS-ANTHRACIS

Bacillus anthracis produces a gamma-linked poly-D-glutamic acid capsul e that is essential for virulence. A 6.2kb fragment of B. anthracis DN A (cap), when present in Escherichia coli, produces a capsular polymer that is immunologically identical to that produced by B. anthracis. B y immunodiffusion analysis of E. coli strains carrying varying portion s of the cap region, we identified a novel gene (dep) responsible for degradation of the capsular polymer of B. anthracis. The simultaneous presence of the cap region and the dep gene caused production of low-m olecular-weight, degraded capsular polymer both in E. coli and in B. a nthracis, whereas the cap region alone caused production of a high-mol ecular-weight capsule. The dep gene mapped immediately downstream of t he cap region within a 1.8 kb fragment and was transcribed in the same direction. This fragment was sequenced and a 1401 bp open reading fra me (ORF) was found that is predicted to encode a peptide with molecula r weight of 51 460. By in vitro transcription-translation analysis, th is ORF was shown to be the dep gene product. The deduced amino acid se quence of the dep product has sequence similarity to E. coli and mamma lian gamma-glutamyltranspeptidase (GGT). However, the Dep protein did not have GGT activity. The Dep protein appears to be an enzyme that ca talyses the hydrolysis of the poly-D-glutamic acid capsule. Although t he biological functions of the dep gene are unknown, it is possible th at low-molecular-weight, diffusible polyglutamates produced through th e action of the dep gene may act to inhibit host defence mechanisms.